Civil engineering challenges of the Einstein Telescope project. An underground observatory for gravitational wave detection

Abstract

The Einstein Telescope (ET) is a proposed underground facility designed to enhance gravitational wave detection by coupling low and high frequency interferometers in an arm length up to 10–15 km. This increase in sensitivity is mainly driven by increasing the interferometer arm lengths, compared to the current generation of 3–4 km arm length. Additionally, by situating the facility deep underground it will benefit from the enhanced seismic and environmental noise isolation that subsurface conditions could provide. The complexity of such a scientific ambition introduces unique challenges for the design of civil engineering works required, particularly given that different sites are proposed. As part of a collaboration agreement with the research funding institutions, Civil Engineering experts at the European Laboratory for Particle Physics (CERN) have been invited to provide technical advice services on key aspects such as civil engineering design strategies and cost estimation methodologies that will contribute to the definition of the Technical Design Report (TDR). This paper, authored from CERN’s independent perspective in collaboration with the Engineering Department of ETO (Einstein Telescope Organisation), presents a structured analysis of the key challenges and opportunities involved in specifying a large-scale underground infrastructure project. The driving requirements of scientific complexity coupled with the analysis of local site conditions make the evaluation of civil engineering design performance particularly challenging. Through comparative analysis of previous large-scale case studies and CERN’s internal design approaches, the study highlights critical aspects that may require specific construction solutions to be developed. To address the complexity of comparing design options, the paper also examines the integration of parametric design and automation tools, specifically through the use of Grasshopper, a visual programming tool. The paper also reflects on strategic implications for a broader project, including site selection parameters, cost profiling and risk management strategies in early design stages.